Oxalic acid treatment of foil

ABSTRACT

Treatment of as-rolled foil, first with oxalic acid and thereafter with heating.

Unlted States Patent [1 1 [111 3,893,872

Eiland July 8, 1975 [54] OXALIC ACID TREATMENT OF FOIL 1,723,067 8/ 1929 Pacz l48/6.l4 A 2,01 ,424 9 1935 148 6 1751 Invent: Ehrlich Eiland Lwer Bum, 3,542,388 12/1970 Russel l48/6.l4 A 3,573,997 4/1971 Plaxton 148/6.l6 [73] Assignee: Aluminum Company of America,

Plttsburgh Primary Examiner-Thomas .1. Herbert, Jr. [22] Filed: Dec. 21, 1972 Assistant Examiner-Bruce H. Hess [2] AppL NO: 317,106 Attorney, Agent, or Firm-Abram W. l-latcher; John P.

Taylor [52] US. Cl. 148/6.14 A; 148/627 [51] Int. Cl. C23f 7/00 [58] Field of Search 148/6.l4 A, 6.27; 117/48, [57] 7 ABSTRACT 117/148 47 H Treatment of as-tolled foil, first with oxalic acid and l 5 6] References Cited thereafter with heating.

UNITED STATES PATENTS 4 main, No Drawings 1.5545183 9/1925 Bailey et a1. 148/627 OXALIC ACID TREATMENT OF FOIL BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to treatment of foil. More particularly, it relates to a process for treating foil to provide good adhesion of inks. coatings and films applied thereto.

2. Description of the Prior Art As-rolled foil, particularly aluminum foil, has a resi-v due of rolling lubricant thereon which prevents proper adhesion of subsequently applied inks, wash coats, adhesives, resins, lacquers and the like. When I say asrolled foil. I am using the term in its conventional meaning, that is, foil in the state in which it exists after being rolled to foil thickness and before annealing. By aluminum. l mean'aluminum and aluminum base alloys containing at least 50% by weight aluminum. Acids,

such as phosphoric acid, which are sometimes used on.

foil to promote ink or coating adhesion are to some extent objectionable because they are affected by humid or wet conditions and as a result adhesion of the inks or coatings is markedly reduced.

SUMMARY OF THE INVENTION After extended investigation I have found that these problems of a lubricant residue and a surface not suited for adherence of applied coatings can be substantially eliminated by applying oxalic acid to as-rolled foil and thereafter heating the foil to which the oxalic acid has been applied. The oxalic acid is preferably applied from a solution or dispersion. Preferred organic dispersants include ethyl alcohol and cellosolve. The concentration of oxalic acid is not critical. Amounts of from as low as 0.0l% have some advantage, and saturated dispersions are also effective.

In the heating step which follows the oxalic acid treatment, preferred temperatures vary from as low as about lF to as high as about 750F, the optimum being 200-750F, although generally a longer heating period is desirable when a low temperature is employed. Usually only a few seconds heating, for example, about l060, will suffice, although longer heating is not harmful and is sometimes advantageous for particular end results such as those which require annealing.

Advantageously according to my invention, the oxalic acid may be sprayed onto the foil, for example, at the rewind side ofa rolling mill. If desired, it may be applied using a conventional coater-laminator. A further advantage of treating foil with oxalic acid and then heating it in accordance with the invention is the imparting of a water wettability to the foil after it is heated. Treatment with oxalic acid also reduces furnace time when an annealed foil product receptive to applied coatings is desired.

The oxalic acid may be applied to one or both sides ofthe foilv It may be applied in a lubricant, for example, in an oil-base lubricant such as mineral oil or in a water-based lubricant, if desired. The preferred concentration is from about 0.01% by weight to about by weight and the preferred coating amount from about 0.05 to about 0.30 mg/ft of surface.

DESCRIPTION OF THE PREFERRED "EMBODIMENTS The following examples areillustrative of the invention.

Example'l coated on one side of as-rolled unannealed l aluminum foil 0.00035 in. thick and dried at 350F for l5 seconds. Nitrocellulose may then be applied to the treated surface and dried. Good adherence is exhibited.

Example 2 An 0.063% solution of oxalic acid in cellosolve may be applied to unannealed as-rolled l 100 aluminum foil with a No. 4 wire wound bar (0.004-in. diameter wire). The coated foil may then be heated at 450F for l minute to give a wettable foil with good adhesion for inks under dry conditions.

Example 3 An 0.1% solution of oxalic acid in cellosolve may be sprayed onto both sides of 1145 aluminum foil on the rewind side of a rolling mill after the foil has been rolled to about 0.0004 inch in thickness. Coils of the foil may then be held at 250F for 48 hours. The foil may be subsequently coated with lacquer, which adheres well.

Example 4 An 0.2% solution of oxalic acid in cellosolve may be applied with a line roll on a coater-laminator to 0.001-inch 1145 as-rolled foil. The web may be rewound into coils without drying. The amount of oxalic acid thus applied totals about 0.3 mg/ft or 0.15 mg/ft per side, on a dry basis. One coil so treated was held at 250F for 48 hours. Another was heated for 8 hours, with the maximum oven temperature reaching 750F. For comparison, a similar coil without oxalic acid was heated in the same manner.

The as-rolled foil held at 250F gave excellent adhesion to epoxy, vinyl and polyester coatings. When the residual cellosolve was dried off, excellent adhesion to inks and polyethylene was obtained. The oxalic acidtreated foil subjected to treatment to the higher temperature had better wettability than the control or comparison oxalic acid-free coil. Adhesion thereof of inks and polyethylene was substantially better than it was for the control foil which was not treated with oxalic acid.

While the invention has been described in terms of preferred embodiments, the claims appended thereto are intended to encompass all embodiments which fall within the spirit of the invention.

Having thus described my invention and certain preferred embodiments thereof, I claim:

1. A process for improving the susceptibility of aluminum foil for adhesion of coatings applied thereto which comprises treating as-rolled foil with from about 0.05 mg/ft to about 0.30 mg/ft oxalic acid to replace residual lubricant on the surface of said foil therewith and thereafter heating the treated foil to a temperature of from 100 to 750F, thereby removing said acid from said surface by volatilization and improving its susceptibility to adherence of inks and lacquers thereto.

2. The process of claim 1 wherein the oxalic acid comprises a solution of oxalic acid in ethyl alcohol or cellosolve.

3. The process of claim 1 wherein the oxalic acid is dispersed in a lubricant.

4. A process for improving ink and lacquer adhesion to aluminum foil which comprises coating as-rolled alu- 

1. A PROCESS FOR IMPROVING THE SUSCEPTIBILITY OF ALLUMINUM FOIL FOR ADHENSION FOR COATING APPLIED THERETO WHICH COMPRISES TREATING AS-ROLLED FOIL WITH FROM ABOUT 0.05 MG/FT2 TO ABOUT 0.30 MG/FT2 OXALIC ACID TO REPLACE RISIDUAL LUBRICANT ON THE SURFACE OF SAID FOIL THEREWITH AND THEREAFTER HEATING THE TREATED FOUL TO A TEMPERATURE OF FROM 100* TO 750*F, THEREBY REMOVING SAID ACID FROM SAID SURFACE BY VOLATILIZATION AND IMPROVING IT SUSCEPTIBILITY TO ADHERENCE OF INKS AND LAQUERS
 2. The process of claim 1 wherein the oxalic acid comprises a solution of oxalic acid in ethyl alcohol or cellosolve.
 3. The process of claim 1 wherein the oxalic acid is dispersed in a lubricant.
 4. A process for improving ink and lacquer adhesion to aluminum foil which comprises coating as-rolled aluminum foil with an organic dispersion consisting of from about 0.01 to about 10% by weight oxalic acid in ethyl alcohol or cellosolve and thereafter heating the foil at a temperature of from about 100* to about 750*F. 